Printed circuit board and method of manufacturing the same

ABSTRACT

A base insulating layer is formed on a suspension body, and write wiring traces and read wiring traces are formed on the base insulating layer. The write wiring trace and the read wiring traces are formed on a body region of the base insulating layer, and the write wiring trace is formed on an auxiliary region of the base insulating layer. The base insulating layer is bent along a bend portion. This causes the write wiring trace to be positioned above the write wiring trace.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a printed circuit board and a method ofmanufacturing the same.

2. Description of the Background Art

Actuators are employed in drives such as hard disk drives. Such anactuator includes an arm arranged rotatably with respect to a rotationshaft and a suspension board used for a magnetic head that is attachedto the arm. The suspension board is a printed circuit board forpositioning the magnetic head with a desired track of a magnetic disk.

FIG. 11 is a vertical sectional view of a conventional suspension board(see JP 2004-133988 A, for example).

In the suspension board 910, a first insulating layer 904 is formed on ametal substrate 902. A write wiring trace W12 and a read wiring traceR12 are formed to be spaced apart from each other by a distance L1 onthe first insulating layer 904.

A second insulating layer 905 is formed on the first insulating layer904 to cover the write wiring trace W12 and the read wiring trace R12.On the second insulating layer 905, a write wiring trace W11 is formedat a position above the read wiring trace R12, and a read wiring traceR11 is formed at a position above the write wiring trace W12.

Each of the distance between the read wiring trace R11 and the writewiring trace W12 that are positioned one above the other and thedistance between the read wiring trace R12 and the write wiring traceW11 that are positioned one above the other is L2.

In the suspension board 910 having the foregoing configuration, thedistances between the write wiring traces W11, W12 and the read wiringtrace R11 are substantially equal to the distances between the writewiring traces W11, W12 and the read wiring trace R12, respectively.Accordingly, it is considered that the magnitude of inducedelectromotive forces generated in the read wiring traces R11, R12 aresubstantially equal when write currents pass through the write wiringtraces W11, W12. This allows a crosstalk between the write wiring tracesW11, W12 and the read wiring traces R11, R12 to be reduced.

In recent years, it is desired to reduce characteristic impedance of thewiring traces in order to achieve lower power consumption of electronicequipment.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to provide a printed circuit boardin which characteristic impedance of wiring traces can be reduced and amethod of manufacturing the same.

(1) According to an aspect of the present invention, a printed circuitboard includes a metal support substrate, a base insulating layerarranged to have a body region formed on the metal support substrate andan auxiliary region formed to project toward the outside of the metalsupport substrate, a first wiring trace provided to continuously extendon the body region and the auxiliary region of the base insulatinglayer, a second wiring trace provided to extend on the body region ofthe base insulating layer, a first cover insulating layer provided onthe body region of the base insulating layer to cover a portion of thefirst wiring trace and the second wiring trace on the body region of thebase insulating layer, and a second cover insulating layer provided onthe auxiliary region of the base insulating layer to cover a portion ofthe first wiring trace on the auxiliary region of the base insulatinglayer, wherein the base insulating layer is bent such that the bodyregion and the auxiliary region overlap each other to cause the portionof the first wiring trace on the auxiliary region to be opposite to aportion of the second wiring trace with the first and second coverinsulating layers sandwiched therebetween.

In the printed circuit board, the body region of the base insulatinglayer is formed on the metal support substrate, and the auxiliary regionof the base insulating layer is formed to project toward the outside ofthe metal support substrate. The first wiring trace is provided tocontinuously extend on the body region and the auxiliary region of thebase insulating layer. The second wiring trace is provided to extend onthe body region of the base insulating layer. The first cover insulatinglayer is formed on the body region of the base insulating layer to coverthe portion of the first wiring trace on the body region of the baseinsulating layer and the second wiring trace. The second cover insultinglayer is provided on the auxiliary region of the base insulating layerto cover the portion of the first wiring trace on the auxiliary regionof the base insulating layer.

In addition, the base insulating layer is bent such that the body regionand the auxiliary region overlap each other to cause the portion of thefirst wiring trace on the auxiliary region of the base insulating layerto be opposite to the portion of the second wiring trace with the firstand second cover insulating layers sandwiched therebetween.

In this case, an area in which the first and second wiring traces areopposite to each other can be increased as compared with a case wherethe first and second wiring traces are arranged on a common plane. Thisincreases capacitance generated by the first and second wiring traces.As a result, characteristic impedance of the first and second wiringtraces can be reduced.

Moreover, the first and second wiring traces provided on the common baseinsulating layer can be formed in common steps in the manufacture. Thisreduces the characteristic impedance of the first and second wiringtraces without complicating the manufacturing steps.

Furthermore, the first and second cover insulating layers arrangedbetween the first and second wiring traces avoid an excessively shortdistance between the first and second wiring traces. Accordingly,transmission loss of signals transmitted through the first and secondwiring traces is prevented from increasing due to the proximity effect.

(2) The portion of the first wiring trace and the portion of the secondwiring trace that are opposite to each other may each have a linearshape.

In this case, the portion of the first wiring trace on the auxiliaryregion and the portion of the second wiring trace can be easily causedto be opposite to each other. This allows simplified manufacturingsteps.

(3) The portion of the first wiring trace and the portion of the secondwiring trace that are opposite to each other may each have a curvedshape.

In this case, the area in which the first wiring trace and the secondwiring trace are opposite to each other can be increased. This furtherreduces the characteristic impedance of the first and second wiringtraces.

(4) The base insulating layer may be bent at a boarder line between thebody region and the auxiliary region and the base insulating layer maybe bent at a portion between the boarder line and the portion of thefirst wiring trace to cause the portion of the first wiring trace to beopposite to the portion of the second wiring trace.

In this case, the base insulating layer as well as the first and secondcover insulating layers are arranged between the first and second wiringtraces. This reliably prevents an excessively short distance between thefirst and second wiring traces. Accordingly, transmission loss ofsignals transmitted through the first and second wiring traces isreliably prevented from increasing due to the proximity effect.

(5) The printed circuit board may further include a head provided on themetal substrate for reading and writing signals, wherein the first andsecond wiring traces are electrically connected to the head.

In this case, the printed circuit board can be used as a suspensionboard of a drive such as a hard disk drive.

(6) According to another aspect of the present invention, a method ofmanufacturing a printed circuit board includes the steps of laminating abase insulating layer on a metal support substrate such that a bodyregion of the base insulating layer is positioned on the metal supportsubstrate and an auxiliary region of the base insulating layer projecttoward the outside of the metal support substrate, forming a firstwiring trace that is arranged to continuously extend on the body regionand the auxiliary region of the base insulating layer and forming asecond wiring trace that is arranged to extend on the body region of thebase insulating layer, forming a first cover insulating layer on thebody region of the base insulating layer to cover a portion of the firstwiring trace and the second wiring trace on the body region of the baseinsulating layer, and forming a second cover insulating layer on theauxiliary region of the base insulating layer to cover a portion of thefirst wiring trace on the auxiliary region of the base insulating layer,and bending the base insulating layer such that the body region and theauxiliary region overlap each other to cause the portion of the firstwiring trace on the auxiliary region to be opposite to a portion of thesecond wiring trace with the first and second cover insulating layerssandwiched therebetween.

In the manufacturing method of the printed circuit board, the baseinsulating layer is laminated on the metal support substrate such thatthe body region of the base insulating layer is positioned on the metalsupport substrate and the auxiliary region of the base insulating layerprojects toward the outside of the metal support substrate. The firstwiring trace is formed to continuously extend on the body region and theauxiliary region of the base insulating layer, and the second wiringtrace is formed to extend on the body region of the base insulatinglayer. The first cover insulating layer is formed on the body region ofthe base insulating layer to cover the portion of the first wiring traceon the body region of the base insulating layer and the second wiringtrace, and the second cover insulting layer is provided on the auxiliaryregion of the base insulating layer to cover the portion of the firstwiring trace on the auxiliary region of the base insulating layer.

In addition, the base insulating layer is bent such that the body regionand the auxiliary region overlap each other to cause the portion of thefirst wiring trace on the auxiliary region of the base insulating layerto be opposite to the portion of the second wiring trace with the firstand second cover insulating layers sandwiched therebetween.

In this case, an area in which the first and second wiring traces areopposite to each other can be increased as compared with a case wherethe first and second wiring traces are arranged on a common plane. Thisincreases capacitance generated by the first and second wiring traces.As a result, characteristic impedance of the first and second wiringtraces can be reduced.

Moreover, the first and second wiring traces are provided on the commonbase insulating layer. Therefore, the first and second wiring traces canbe formed in common steps in the manufacture. This reduces thecharacteristic impedance of the first and second wiring patterns withoutcomplicating the manufacturing steps.

Furthermore, the first and second cover insulating layers arrangedbetween the first and second wiring traces avoid an excessively shortdistance between the first and second wiring traces. Accordingly,transmission loss of signals caused by the first and second wiringtraces is prevented from increasing due to the proximity effect.

According to the present invention, the area in which the first andsecond wiring traces are opposite to each other can be increased. Thisincreases the capacitance generated by the first and second wiringtraces. As a result, the characteristic impedance of the first andsecond wiring traces can be reduced.

Other features, elements, characteristics, and advantages of the presentinvention will become more apparent from the following description ofpreferred embodiments of the present invention with reference to theattached drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofthe invention, will be better understood when read in conjunction withthe appended drawings. For the purpose of illustrating the invention,there are shown in the drawings embodiments which are presentlypreferred. It should be understood, however, that the invention is notlimited to the precise arrangements and instrumentalities shown.

In the drawings:

FIG. 1 is a top view of a suspension board according to one embodimentof the present invention;

FIG. 2 is a sectional view of the suspension board taken along the lineA-A of FIG. 1;

FIG. 3 is a sectional view of the suspension board with a baseinsulating layer being bent;

FIG. 4 is a vertical sectional view showing steps of manufacturing thesuspension board;

FIG. 5 is a diagram for explaining problems that may occur when writewiring traces are hierarchically arranged one above the other;

FIG. 6 is a schematic sectional view of the suspension board that isprepared as a comparative example;

FIG. 7 is a sectional view for explaining a modification of thesuspension board;

FIG. 8 shows a plan view and a sectional view for explaining anothermodification of the suspension board;

FIG. 9 shows a plan view and a section view for explaining the anothermodification of the suspension board;

FIG. 10 shows a plan view and a section view for explaining the anothermodification of the suspension board; and

FIG. 11 is a vertical sectional view of a conventional suspension board.

DETAILED DESCRIPTION OF THE INVENTION

Description will be made of a printed circuit board and a method ofmanufacturing the same according to one embodiment of the presentinvention while referring to the drawings. Hereinafter, description ismade of the configuration of a suspension board used in an actuator of ahard disk drive as the printed circuit board according to the oneembodiment of the present invention and the method of manufacturing thesame.

(1) Configuration of Suspension Board

FIG. 1 is a top view of the suspension board according to one embodimentof the present invention, and FIG. 2 is a sectional view of thesuspension board taken along the line A-A of FIG. 1.

As shown in FIG. 1, the suspension board 1 includes a suspension body 10formed of a long-sized metal substrate. A base insulating layer 41 isformed in a predetermined region on the suspension body 10. Write wiringtraces W1, W2 and read wiring traces R1, R2 are formed on the baseinsulating layer 41. A cover insulating layer is formed on the baseinsulating layer 41 to cover the write wiring traces W1, W2 and the readwiring traces R1, R2 as described below.

The suspension body 10 includes a tip region P1, a rear end region P2,and an intermediate region P3 that extends in a long-sized shape betweenthe tip region P1 and the rear end region P2.

At the tip region P1 of the suspension body 10, a U-shaped opening 11 isformed, thereby providing a magnetic head supporting portion(hereinafter referred to as a tongue) 12. The tongue 12 is bent alongthe broken line R to form a predetermined angle with respect to thesuspension body 10. Four electrode pads 21, 22, 23, 24 are formed at anend of the tongue 12. A hole H is formed in the tip region P1 of thesuspension body 10.

Four electrode pads 31, 32, 33, 34 are formed in the rear end region P2of the suspension body 10. The electrode pads 21 to 24 on the tongue 12and the electrode pads 31 to 34 at the rear end region P2 of thesuspension body 10 are electrically connected to one another through thewrite wiring traces W1, W2 and the read wiring traces R1, R2,respectively.

Part of the base insulating layer 41 is provided to project toward theoutside of one side of the intermediate region P3 of the suspension body10. A portion of the base insulating layer 41 on the suspension body 10is referred to as a body region 51, and a portion of the base insulatinglayer 41 that projects toward the outside of the suspension body 10 isreferred to as an auxiliary region 52. A bend portion B1 is provided atboundary between the body region 51 and the auxiliary region 52. Alinear groove may be formed or a linear mark may be provided at the bendportion B1. There may be nothing provided at the bend portion B1 if thebase insulating layer 41 can be easily bent.

The write wiring trace W2 and the read wiring traces R1, R2 are providedto extend on the body region 51 of the base insulating layer 41. Thewrite wiring trace W1 is provided to continuously extend from the bodyregion 51 of the base insulating layer 41 to go through the auxiliaryregion 52 and then return to the body region 51.

The write wiring trace W2 and the read wiring traces R1, R2 linearlyextend in a portion of the body region 51 adjacent to the auxiliaryregion 52. On the auxiliary region 52 of the base insulating layer 41,the write wiring trace W1 linearly extends in parallel with the writewiring trace W2.

As shown in FIG. 2, the base insulating layer 41 is formed on thesuspension body 10, and the write wiring traces W1, W2 and the readwiring traces R1, R2 are formed on the base insulating layer 41. Thewrite wiring trace W2 and the read wiring traces R1, R2 are formed onthe body region 51 of the base insulting layer 41, and the write wiringtrace W1 is formed on the auxiliary region 52 of the base insulatinglayer 41.

The width of each of the write wiring traces W1, W2 and the read wiringtraces R1, R2 is set sufficiently larger than the thickness of each ofthe write wiring traces W1, W2 and the read wiring traces R1, R2. Adistance T1 between the bend portion B1 and the write wiring trace W1 isset equal to a distance T2 between the bend portion B1 and the writewiring trace W2.

A cover insulating layer 42 a is formed to cover the write wiring tracesW1, W2 and the read wiring traces R1, R2 on the body region 51 of thebase insulating layer 41. A cover insulating layer 42 b is formed tocover the write wiring trace W1 on the auxiliary region 52 of the baseinsulating layer 41. Note that the cover insulating layers 42 a, 42 bare integrated with each other at intersection portions of the writewiring trace W1 and the bend portion B1.

The base insulating layer 41 is bent along the bend portion B1 in thesuspension board 1 of the present embodiment. FIG. 3 is a sectional viewof the suspension board 1 with the base insulating layer 41 being bent.

As described above, the distance T1 between the bend portion B1 and thewrite wiring trace W1 and the distance T2 between the bend portion B1and the write wiring trace W2 are equal to each other. Therefore, thebase insulating layer 41 is bent along the bend portion B1 to cause thewrite wiring trace W1 to be positioned above the write wiring trace W2as shown in FIG. 3. In this state, the cover insulating layer 42 a andthe cover insulating layer 42 b are fixed to each other.

(2) Manufacturing Method

Next, description is made of a manufacturing method of the suspensionboard 1. FIG. 4 is a vertical sectional view showing steps ofmanufacturing the suspension board 1. FIG. 4 shows manufacturing stepsof a portion corresponding to the cross section taken along the line A-Aof FIG. 1.

First, the base insulating layer 41 made of polyimide, for example, islaminated on the suspension body 10 made of stainless steel, forexample, using an adhesive as shown in FIG. 4 (a).

The thickness of the suspension body 10 is not less than 5 μm and notmore than 50 μm, for example, and preferably not less than 10 μm and notmore than 30 μm. Another metal such as aluminum, or an alloy instead ofstainless steel may be employed as the suspension body 10.

The thickness of the base insulating layer 41 is not less than 1 μm andnot more than 15 μm, for example, and preferably not less than 2 μm andnot more than 12 μm. Another insulating material such as epoxy insteadof polyimide may be employed as the base insulating layer 41.

Next, the write wiring traces W1, W2 and the read wiring traces R1, R2made of copper, for example, are formed on the base insulating layer 41as shown in FIG. 4 (b). In this case, the write wiring trace W1 isprovided to continuously extend from the body region 51 of the baseinsulating layer 41 to go through the auxiliary region 52 and thenextend to the body region 51.

The write wiring traces W1, W2 may be formed using a semi-additivemethod, for example, and may be formed using another method such as asubtractive method.

The width of each of the write wiring traces W1, W2 is larger than thethickness of each of the write wiring traces W1, W2, and is preferablynot more than 40 times as large as the thickness of each of the writewiring traces W1, W2. Moreover, the width of each of the write wiringtraces W1, W2 is more preferably not more than 20 times as large as thethickness of each of the write wiring traces W1, W2.

The thickness of each of the write wiring traces W1, W2 and the readwiring traces R1, R2 is not less than 3 μm and not more than 16 μm, forexample, and preferably not less than 6 μm and not more than 13 μm. Thewidth of each of the write wiring traces W1, W2 and the read wiringtraces R1, R2 is not less than 20 μm and not more than 200 μm, forexample, and preferably not less than 30 μm and not more than 100 μm.

The material for the write wiring traces W1, W2 and the read wiringtraces R1, R2 is not limited to copper. For example, another metal suchas gold (Au) and aluminum or an alloy such as a copper alloy and analuminum alloy may be used.

Next, the cover insulating layer 42 b is formed on the auxiliary region52 of the base insulating layer 41 to cover the write wiring trace W1,and the cover insulating layer 42 a is formed on the body region 51 ofthe base insulating layer 41 to cover the write wiring traces W1, W2 andthe read wiring traces R1, R2 as shown in FIG. 4 (c).

Then, the base insulating layer 1 is bent along the bend portion B1 asshown in FIG. 4 (d). The cover insulating layer 42 a and the coverinsulating layer 42 b are fixed to each other using the adhesive or thelike.

(3) Effects

The write wiring traces W1, W2 are arranged one above the other in thesuspension board 1 according to the present embodiment. In addition, thewidth of each of the write wiring traces W1, W2 is set sufficientlylarger than the thickness thereof.

Here, characteristic impedance of the write wiring traces W1, W2 becomessmaller with increasing capacitance of the write wring traces W1, W2.The capacitance becomes larger with increasing an area in which thewrite wiring trace W1 and the write wiring trace W2 are opposite to eachother. That is, the characteristic impedance of the write wiring tracesW1, W2 becomes smaller with increasing the area in which the writewiring trace W1 and the write wiring trace W2 are opposite to eachother.

Therefore, the write wiring traces W1, W2 are arranged one above theother and the width of each of the write wiring traces W1, W2 is setsufficiently larger than the thickness thereof, so that the area inwhich the write wiring traces W1, W2 are opposite to each other isincreased as compared with a case where the write wiring traces W1, W2are arranged on a common plane. Accordingly, the characteristicimpedance of the write wiring traces W1, W2 is reduced as compared withthe case where the write wiring traces W1, W2 are arranged on the commonplane.

Note that the write wiring traces W1, W2 are formed on the common baseinsulating layer 41 and the base insulating layer 41 is bent to causethe write wiring traces W1, W2 to be arranged one above the other in thepresent embodiment. In this case, the write wiring traces W1, W2 can beformed in respective common steps, and the cover insulating layers 42 a,42 b can be formed in respective common steps. Accordingly, the numberof the manufacturing steps can be reduced as compared with a case wherethe plurality of layers are sequentially formed to cause the writewiring traces W1, W2 to be hierarchically arranged one above the other.

In addition, the following problem may occur when the write wiringtraces W1, W2 are hierarchically arranged one above the other.

FIG. 5 is a diagram for explaining problems that may occur when thewrite wiring traces W1, W2 are hierarchically arranged one above theother.

In the example of FIG. 5, the write wiring trace W1 is formed on thecover insulating layer 42 a above the write wiring trace W2, and thecover insulating layer 42 b is formed on the cover insulating layer 42 ato cover the write wiring trace W1.

In practice, a portion of the cover insulating layer 42 a formed abovethe write wiring trace W2 is curved. Since the write wiring trace W1 isformed on the curved portion of the cover insulating layer 42 a, thewrite wiring trace W1 is also curved along the insulating layer 42 a. Inthis case, currents flowing through the write wiring traces W1, W2 areconcentrated in edge portions of the write wiring traces W1, W2 due tothe proximity effect. This leads to higher impedance of the write wiringtraces W1, W2, resulting in larger transmission loss of signals causedby the write wiring traces W1, W2.

On the other hand, since both the write wiring traces W1, W2 are formedon the flat base insulating layer 41, the write wiring traces W1, W2 arenot curved in the present embodiment. Therefore, an increase in thetransmission loss can be prevented while the write wiring traces W1, W2can be arranged one above the other.

Moreover, the two layers, which are the cover insulating layers 42 a, 42b, are arranged between the write wiring trace W1 and the write wiringtrace W2 in the present embodiment. In this case, a distance between thewrite wiring traces W1, W2 is prevented from being excessively short.This sufficiently suppresses the increase in the transmission loss ofthe signals caused by the write wiring traces W1, W2 due to theproximity effect.

Furthermore, the cover insulating layers 42 a, 42 b can be formed in thecommon steps. This sufficiently suppresses the increase in thetransmission loss of the signals caused by the write wiring traces W1,W2 in a shorter manufacturing period than a case where the thickness ofone insulating layer is increased.

(4) Inventive Example and Comparative Example (4-1) Inventive Example

The suspension board 1 shown in FIGS. 1 and 2 was prepared as aninventive example. Note that copper was employed as the material for thewrite wiring traces W1, W2, stainless steel was employed as the materialfor the suspension body 10, and polyimide was employed as the materialfor the base insulating layer 41 and the cover insulating layers 42 a,42 b. The width of each of the write wiring traces W1, W2 was 35 μm, andthe thickness thereof was 18 μm.

The thickness of the suspension body 10 was 18 μm, the thickness of thebase insulating layer 41 was 10 μm, and the thickness of each of thecover insulating layers 42 a, 42 b was 5 μm.

(4-2) Comparative Example

FIG. 6 is a schematic sectional view of a suspension board that isprepared as a comparative example. FIG. 6 shows a cross section of aportion corresponding to the cross section taken along the line A-A ofFIG. 1 in the suspension board of the comparative example. Thesuspension board 100 of FIG. 6 is different from the suspension board 1of the inventive example in the following points.

In the suspension board 100, the write wiring trace W1 was formed on thebody region 51 of the base insulating layer 41. In addition, theauxiliary region 52 was not provided in the base insulating layer 41,and the base insulating layer 41 was not bent. Note that the distancebetween the write wiring trace W1 and the write wiring trace W2 was 20μm.

(4-3) Evaluation

In the suspension boards 1, 100 of the inventive example and thecomparative example, the characteristic impedance of the write wiringtraces W1, W2 was examined.

The results show the characteristic impedance of the write wiring tracesW1, W2 was about 40Ω in the suspension board 1 of the inventive example.On the other hand, the characteristic impedance of the write wiringtraces W1, W2 was about 80Ω in the suspension board 100 of thecomparative example.

Accordingly, it can be seen that the characteristic impedance of thewrite wiring traces W1, W2 was reduced by arranging the write wiringtraces W1, W2 one above the other as compared with the case where thewrite wiring traces W1, W2 were arranged on the common plane.

(5) Modifications (5-1)

FIG. 7 is a sectional view for explaining a modification of thesuspension board 1 according to the foregoing embodiment.

In the example of FIG. 7, only an end of the cover insulating layer 42 bis bonded to the cover insulating layer 42 a with an adhesive layer 55sandwiched therebetween such that an air layer A1 is formed between thecover insulating layers 42 a, 42 b while the base insulating layer 41 isbent along the bend portion B1.

(5-2)

FIG. 8 shows a plan view and a sectional view for explaining anothermodification of the suspension board 1 according to the foregoingembodiment. Note that FIG. 8 (a) shows the auxiliary region 52 of thebase insulating layer 41 and an adjacent portion thereof, and FIG. 8 (b)shows a cross section taken along the line B-B of FIG. 8 (a).Description is made of a suspension board 1 a of FIG. 8 while referringto differences from the suspension board 1 of the foregoing embodiment.

In the suspension board 1 a of FIG. 8, the write wiring trace W2 and theread wiring traces R1, R2 each extend in a curved shape in a portion ofthe body region 51 adjacent to the auxiliary region 52. The write wiringtrace W1 extends in a curved shape on the auxiliary region 52 of thebase insulating layer 41. Curved portions of the write wiring traces W1,W2 have the same shape.

A bend portion B2 is provided at boundary between the body region 51 andthe auxiliary region 52 of the base insulating layer 41. In addition, abend portion B3 is provided in parallel with the bend portion B2 in theauxiliary region 52 of the base insulating layer 41.

In the suspension board 1 a, the base insulating layer 41 is bent alongthe bend portions B2, B3.

FIG. 9 (a) shows a plan view of the suspension board 1 a with the baseinsulating layer 41 being bent along the bend portion B2, and FIG. 9 (b)shows a cross section taken along the line C-C of FIG. 9 (a). FIG. 10(a) shows a plan view of the suspension board 1 a with the baseinsulating layer 41 being bent along the bend portions B2, B3, and FIG.10 (b) shows a cross section taken along the line D-D of FIG. 10 (a).

As shown in FIGS. 9 (a) and (b), the write wiring trace W1 and the writewiring trace W2 hardly overlap each other when the base insulating layer41 is bent along the bend portion B2. In this case, since the area inwhich the write wiring trace W1 and the write wring trace W2 areopposite to each other is small, the characteristic impedance of thewrite wiring traces W1, W2 cannot be sufficiently reduced.

Therefore, the base insulating layer 41 is further bent along the bendportion B3 as shown in FIGS. 10 (a) and (b). This causes the writewiring trace W1 and the write wiring trace W2 to overlap each other.Thus, the area in which the write wiring trace W1 and the write wiringtrace W2 are opposite to each other is increased to sufficiently reducethe characteristic impedance of the write wiring traces W1, W2.

In addition, the base insulating layer 41 is bent along the bendportions B2, B3, so that the base insulating layer 41 is doubled and thecover insulating layers 42 a, 42 b are arranged between the write wiringtraces W1, W2. Accordingly, the distance between the write wiring tracesW1, W2 is more sufficiently ensured, and the increase in thetransmission loss of the signals caused by the write wiring traces W1,W2 due to the proximity effect is more sufficiently suppressed.

(5-3)

While the base insulating layer 41 is bent along the bend portions B2,B3 to cause the portions of the write wiring traces W1, W2 in the curvedshape to overlap each other in the example of FIGS. 8 to 10, theportions of the write wiring traces W1, W2 in the curved shape may becaused to overlap each other by another method.

For example, the curved shape of the write wiring trace W2 formed on thebody region 51 and the curved shape of the write wring trace W1 formedon the auxiliary region 52 are symmetrically set with respect to aboarder line between the body region 51 and the auxiliary region 52. Inthis case, the base insulating layer 41 is bent along the boarder linebetween the body region 51 and the auxiliary region 52 to allow theportions of the write wiring traces W1, W2 in the curved shape tooverlap each other.

(5-4)

In a suspension board in which the write wiring traces W1, W2 arelinearly formed on the auxiliary region 52 and the portion on the bodyregion 51 adjacent to the auxiliary region 52 such as the suspensionboard 1 shown in FIGS. 1 and 2, the base insulating layer 41 may be bentat two portions similarly to the modification shown in FIGS. 7 to 9.

In this case, the thickness of the insulating layer between the writewiring traces W1, W2 is increased, so that the increase in thetransmission loss of the signals caused by the write wiring traces W1,W2 can be sufficiently suppressed.

(6) Correspondences Between Elements in the Claims and Parts inEmbodiments

In the following paragraphs, non-limiting examples of correspondencesbetween various elements recited in the claims below and those describedabove with respect to various preferred embodiments of the presentinvention are explained.

In the foregoing embodiment, the suspension body 10 is an example of ametal support substrate, the write wiring trace W1 is an example of afirst wiring trace, the write wiring trace W2 is an example of a secondwiring trace, the cover insulating layer 42 a is an example of a firstcover insulating layer, the cover insulating layer 42 b is an example ofa second cover insulating layer, and the tongue 12 is an example of ahead.

As each of various elements recited in the claims, various otherelements having configurations or functions described in the claims canbe also used.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing the scope andspirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

1. A printed circuit board comprising: a metal support substrate; a baseinsulating layer arranged to have a body region formed on said metalsupport substrate and an auxiliary region formed to project toward theoutside of said metal support substrate; a first write wiring traceprovided to continuously extend on said body region and said auxiliaryregion of said base insulating layer; a first read wiring trace, asecond read wiring trace and a second write wiring trace provided toextend on said body region of said base insulating layer; a first coverinsulating layer provided on said body region of said base insulatinglayer to cover a portion of said first write wiring trace, said firstread wiring trace, said second read wiring trace and the second writewiring trace on said body region of said base insulating layer; and asecond cover insulating layer provided on said auxiliary region of saidbase insulating layer to cover a portion of said first write wiringtrace on said auxiliary region of said base insulating layer, whereinsaid second write wiring trace is provided at a position closer to saidauxiliary region than to said first and second read wiring traces, andsaid base insulating layer is bent such that said body region and saidauxiliary region overlap each other to cause the portion of said firstwrite wiring trace on said auxiliary region to be opposite to a portionof said second write wiring trace with said first and second coverinsulating layers sandwiched therebetween.
 2. The printed circuit boardaccording to claim 1, wherein the portion of said first write wiringtrace and the portion of said second write wiring trace that areopposite to each other each have a linear shape.
 3. The printed circuitboard according to claim 1, wherein the portion of said first writewiring trace and the portion of said second write wiring trace that areopposite to each other each have a curved shape.
 4. The printed circuitboard according to claim 1, wherein said base insulating layer is bentat a boarder line between said body region and said auxiliary region andsaid base insulating layer is bent at a portion between said boarderline and the portion of said first write wiring trace on said auxiliaryregion to cause the portion of said first write wiring trace on saidauxiliary region to be opposite to the portion of said second writewiring trace.
 5. The printed circuit board according to claim 1, furthercomprising a head provided on said metal support substrate for readingand writing signals, wherein said first and second write wiring tracesare electrically connected to said head.